1. Field of the Invention
The present invention relates to the amine catalysts useful for producing polyurethane foams coated with skin. More particularly, the invention relates to the amine catalysts useful for producing polyurethane foams coated with skin, which emit no bad odor, give excellent moldability, and are free from deterioration of skin and discoloration of covering materials.
2. Description of Related Arts
Polyurethane foams are usually prepared by the reaction of solution A with solution B under high speed mixing agitation, solution A containing polyol, blowing agents, surfactant, catalyst and other promotor and solution B containing polyisocyanate.
Polyurethane foams coated with skin have a wide range of applications. Among them the most common usage is for interior materials of automobile such as for cushion, arm rest, head rest, instrument panel and dash board. These products are usually coated with urethane elastomer, vinyl chloride resin or a complex of ABS and vinyl chloride resins, and frequently they are prepared in a united product.
On the other hand, tertiary amine catalysts, employed in the production of polyurethane foams, are partly lost by evaporation and the rest remains in the product foams. Amine compounds usually have peculiar amine odor which emits a bad smell and imparts bad influences to the working condition or further to the environmental problem. Amine compounds, if left in the foam, may bleed toward the outside of the foam and react with vinyl chloride in the skin to accelerate dehydrochlorination and to discolor the skin. In other instance, halogen compounds such as fire retardant in the foam composition, react with the remaining amine compounds to produce halides which often discolor the skin.
So far, the discoloration of the skin has been avoided by increasing the thickness of the skin to lessen the breed of the amine catalyst, but it brings about a large cost disadvantage. On the other hand, a variety of amine catalysts have been proposed. For example, they include a catalyst which is reactive with raw material isocyanate (Japanese Laid-Open Patent Application No. Sho 58-17115) and a catalyst having a high molecular weight to reduce the breeding speed (Japanese Laid-Open Patent Application No. Sho 54-20099). However, there still remained a problem that amine catalysts which deteriorated and discolored the skin to a lesser degree did not always provide better physical properties of the foam. Thus, most eagerly desired was an amine catalyst which eliminates these problems.
4-Methyl-1-(2-hydroxyalkyl)piperazine has been disclosed by some of the present inventors and is one of the known tertiary amine catalysts. However, there has not been described that the 4-methyl-1-(2-hydroxyalkyl)piperazine is a catalyst useful to prevent deterioration and discoloration of polyurethane products coated with skin, and further there is not found an example in which the compound has been utilized in this field.